The study on LLC series resonant converter for high efficiency & high power density power supply

Abstract

With the recent development of information technology, the markets of power management for telecom, server, and display equipments are gradually increasing. Distributed power system (DPS) is popular in these applications for its high performance, efficiency, and reliability. AC/DC front-end converter is under pressures of continuous increasing efficiency and power density. Therefore, technologies need to be continuously developed to fulfill the future requirements. General power architecture including DPS, which uses AC line as its input source, consists of three stages; (1) power factor correction (PFC) stage to regulate harmonics in the input current; (2) isolated DC/DC stage to provide a galvanic isolation and a stable DC bus voltage or a main output voltage; (3) load converter to tight regulate the output voltage of each load from the bus voltage. Especially, an isolated DC/DC stage is given a great deal of weight on volume and efficiency of the total power system. Therefore, careful attention must be paid to the increase efficiency and power density for an isolated DC/DC stage. Among many topologies, the LLC series resonant converter is one of the most popular topologies in medium to high power applications because of its simple structure, zero voltage switching capability, and wide input range. Therefore, LLC series resonant converter is strong candidate for DC-DC stage. However, some applications require special specifications to achieve high performance of its applications. These specifications make LLC series resonant converter have low efficiency and low power density. In this dissertation, the research is mainly focused on an optimal design and operational method of LLC series resonant converter in isolated DC/DC stage of AC/DC front-end converters, aiming at improving efficiencies and power density. At first, problems related with an output voltage variation specification for AC-DC adapter is discussed and the solution for having high efficien...